ST Questions

Two questions on module ST:
<http://www.haskell.org/ghc/docs/latest/set/sec-st.html>
1. What's the 's' parameter for?
2. Do STRefs get garbage-collected once they're forgotten? For instance,
if I have an action that calls newSTRef, uses the ref, and then forgets
it, and I run the action repeatedly, am I at risk of running out of
memory?
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Ashley Yakeley, Seattle WA